Question

我想过滤今天，周和月的数据。

var data = new DashboardViewModel()
           {
               Today = new State() { Download = db.Download.Where(x => x.Time == DateTime.Today).Count(), Visit = db.Visit.Where(x => x.Time == DateTime.Today).Count() },
               Week = new State() { Download = db.Download.Where(x => x.Time.DayOfYear <= Day && x.Time.DayOfYear >= Day - 7).Count(), Visit = db.Visit.Where(x => x.Time.DayOfYear <= Day && x.Time.DayOfYear >= Day - 7).Count() },
               Month = new State() { Download = db.Download.Where(x => x.Time.DayOfYear <= Day && x.Time.DayOfYear >= Day - 30).Count(), Visit = db.Visit.Where(x => x.Time.DayOfYear <= Day && x.Time.DayOfYear >= Day - 30).Count() },
               Total = new State() { Download=db.Download.Count(),Visit=db.Visit.Count()}
           };

它给出错误：

LINQ to Entities不支持指定的类型成员'DayOfYear'。

如何解决此错误，还是有其他更好的方法可以解决此问题？

Answer 1

问题在于，当LINQ to Entities解析你的lambda表达式并将其转换为SQL时，它不知道'DayOfYear'是什么，以及它如何映射到有效的SQL。这是DbFunctions（v6之前的EF EntityFunctions）的来源，它允许您在LINQ to Entities中使用日期操作函数。例如，要按周过滤，您可以使用：

Week = new State() { 
    Download = db.Download.Where(x => DbFunctions.DiffDays(DbFunctions.TruncateTime(x.Time), Day) <= 7).Count(), 
    Visit = db.Visit.Where(x => DbFunctions.DiffDays(DbFunctions.TruncateTime(x.Time), Day) <= 7).Count() }

TruncateTime从日期中删除时间组件，DiffDays（d1，d2）为您提供2天（d2 - d1）之间的差异。

Answer 2

请参阅此answer：

var ruleDate = Convert.ToDateTime(rule.data).Date;
return jobdescriptions.Where(j.Deadline.Year == ruleDate.Year 
                       && j j.Deadline.Month == ruleDate.Month 
                       && j.Deadline.Day == ruleDate.Day);

根据日，周和月过滤数据

2 个答案: